Glioblastoma multiforme (GBM), the most common and lethal tumor of the adult brain, generally shows chemo- and radioresistance. MicroRNAs (miRs) regulate physiological processes, such as resistance of GBM cells to temozolomide (TMZ). Although miRs are attractive targets for cancer therapeutics, the effectiveness of this approach requires targeted delivery. Mesenchymal stem cells (MSCs) can migrate to the sites of cancers, including GBM. We report on an increase in miR-9 in TMZ-resistant GBM cells. miR-9 was involved in the expression of the drug efflux transporter, P-glycoprotein. To block miR-9, methods were developed with Cy5-tagged anti-miR-9. Dye-transfer studies indicated intracellular communication between GBM cells and MSCs. This occurred by gap junctional intercellular communication and the release of microvesicles. In both cases, anti-miR-9 was transferred from MSCs to GBM cells. However, the major form of transfer occurred with the microvesicles. The delivery of anti-miR-9 to the resistant GBM cells reversed the expression of the multidrug transporter and sensitized the GBM cells to TMZ, as shown by increased cell death and caspase activity. The data showed a potential role for MSCs in the functional delivery of synthetic anti-miR-9 to reverse the chemoresistance of GBM cells.

Mesenchymal stem cells (MSCs) are mostly found around the vasculature system of the adult bone marrow (BM). They function as immune suppressors, express MHC-II, are phagocytic, and support T-cell cytotoxicity. We hypothesize that these contradictory properties of MSCs are important for BM homeostasis and occur partly through antigen presentation (antigen-presenting cells [APCs]) within a narrow window. Indeed, we have verified APC functions of MSCs to recall antigens, Candida albicans and Tetanus toxoid. The target cells have been identified to be CD4+ T cells. APC assays with IFNγ-knockdown MSCs and with anti–IFNγ receptor confirmed that MHC-II expression requires autocrine stimulation by IFNγ. During APC functions, as IFNγ levels become elevated, there was a concomitant decrease in MHC-II on MSCs. This observation was correlated with flow cytometry studies showing a gradual decrease in MHC-II expression as IFNγ levels were increased. The reduced levels of MHC-II correlated with losses in their allogeneic potential, as indicated in mixed lymphocyte reaction. In summary, endogenous and low levels of IFNγ are required for MHC-II expression on MSCs, and for APC functions. APC functions occur during a narrow window before IFNγ levels are increased. The study has implications for BM protection against infection and exacerbated inflammatory responses.

Dormant breast cancers resurge as metastatic disease after a long dormancy period in the bone marrow, where cancer cells interact with mesenchymal stem cells (MSC). However, the nature of early interactions between breast cancer cells and MSCs in the bone marrow microenvironment that facilitate adaptation to a quiescent state remains poorly understood. Here, we report that breast cancer cells prime MSC to release exosomes containing distinct miRNA contents, such as miR-222/223, which in turn promotes quiescence in a subset of cancer cells and confers drug resistance. Building on these results, we developed a novel, nontoxic therapeutic strategy to target dormant breast cancer cells based on systemic administration of MSC loaded with antagomiR-222/223. In an immunodeficient mouse model of dormant breast cancer, this therapy sensitized breast cancer cells to carboplatin-based therapy and increased host survival. Overall, our findings illuminate the nature of the regulatory interactions between breast cancer cells and MSCs in the evolution of tumor dormancy and resurgence in the micrometastatic microenvironment of the bone marrow. Cancer Res; 76(19); 5832–44. ©2016 AACR.

OCT4 is a master transcriptional regulator, which mediates pluripotency in ESCs through inhibition of tissue-specific and promotion of stem cell-specific genes. Suppression of OCT4, along with other regulators of pluripotency, such as SOX2 and NANOG, has been correlated with cell-fate specification and lineage-specific differentiation. Recent reports have shown the expression of OCT4 in adult MSCs but have not ascribed functional homology with ESCs. MSCs are mesoderm-derived cells, primarily resident in adult bone marrow, that undergo lineage-specific differentiation to generate specialized cells such as stroma, fat, bone, and cartilage. We have previously demonstrated the plasticity of MSCs through their ability to generate neuronal cells. Here, we show that OCT4 provides similar regulatory circuitries in human MSCs and ESCs, using chromatin immunoprecipitation-DNA selection and ligation technology and loss-of-function studies. MSCs were found to express the embryonic transcription factors OCT4, NANOG, and SOX2. In addition, OCT4 was found to (a) target similar genes in MSCs and ESCs, (b) promote the expression of MSC-specific genes, and (c) regulate MSC cell cycle progression. The results suggest similar regulatory mechanisms for OCT4 in MSCs and ESCs and have implications regarding MSC plasticity. Disclosure of potential conflicts of interest is found at the end of this article.

Mesenchymal stem cells (MSCs) exhibit immune-suppressive properties, follow a pattern of multilineage differentiation, and exhibit transdifferentiation potential. Ease in expansion from adult bone marrow, as well as its separation from ethical issues, makes MSCs appealing for clinical application. MSCs treated with retinoic acid resulted in synaptic transmission, based on immunostaining of synaptophysin and electrophysiological studies. In situ hybridization indicated that the neurotransmitter gene preprotachykinin-I was expressed in these cells. However, translation of this gene only occurred after stimulation with interleukin (IL)-1α. This effect was blunted by costimulation with IL-1 receptor antagonist. This study reports on the ability of MSCs to be transdifferentiated into neurons with functional synapses with the potential to become polarized towards producing specific neurotransmitters.

Dopamine (DA) neurons derived from stem cells are a valuable source for cell replacement therapy in Parkinson disease, to study the molecular mechanisms of DA neuron development, and for screening pharmaceutical compounds that target DA disorders. Compared with other stem cells, MSCs derived from the adult human bone marrow (BM) have significant advantages and greater potential for immediate clinical application. We report the identification of in vitro conditions for inducing adult human MSCs into DA cells. Using a cocktail that includes sonic hedgehog and fibroblast growth factors, human BM-derived MSCs were induced in vitro to become DA cells in 12 days. Based on tyrosine hydroxylase (TH) expression, the efficiency of induction was determined to be ∼67%. The cells develop a neuronal morphology expressing the neuronal markers NeuN and β III tubulin, but not glial markers, glial fibrillary acidic protein and Olig2. As the cells acquire a postmitotic neuronal fate, they downregulate cell cycle activator proteins cyclin B, cyclin-dependent kinase 2, and proliferating cell nuclear antigen. Molecular characterization revealed the expression of DA-specific genes such as TH, Pitx3, Nurr1, DA transporter, and vesicular monoamine transporter 2. The induced MSCs also synthesize and secrete DA in a depolarization-independent manner. The latter observation is consistent with the low expression of voltage gated Na+ and Ca2+ channels in the induced MSCs and suggests that the cells are at an immature stage of development likely representing DA neuronal progenitors. Taken together, the results demonstrate the ability of adult human BM-derived MSCs to form DA cells in vitro. Disclosure of potential conflicts of interest is found at the end of this article.